Fifteen years of changes in fire ignition frequency in Sardinia (Italy). A rich-get-richer process

Humans have increasingly been affecting fire regimes through changes in the amount and distribution of ignition energy and fuel load. Within the context of global change, recent studies have shown that changes in demography and land use account for far more variability in shaping fire regimes than climatic variations. The objectives of this study are to analyze temporal trends in fire ignitions in selected land use/land cover (LULC) classes in Sardinia (Italy) over the years 2000–2015, and to assess the role of demographic dynamics from 1971 to 2011 over such changes. We identified the LULC types where annual fire frequency is higher or lower than expected from a null model through a ‘fire selectivity index’. Then we analyzed the temporal trend of fire selectivity in all LULC types with linear regressions and tested the role of demographic trends on fire frequency through a two-way contingency table. A general trend of increasing fire occurrence was observed in highly-managed LULC classes, which are mainly located in regions with positive demographic variation; whilst, a decreasing trend of fire occurrence was observed in less human-impacted LULCs, which are preferentially associated to inner regions with negative demographic variation. Results highlight a rich-get-richer process in which anthropogenic LULC classes with highest fire frequency tend to be increasingly selected by fire, whereas in less impacted LULC fire frequency is progressively reduced. The relationship between fire ignitions and demographic processes is of great socio-ecological relevance, because it contributes to clarify the human influence on changing fire regimes.